Flow Sensor With Heated Air Collar

ABSTRACT

A collar is provided for use with a fluid flow sensor to reduce condensation of a moist gas flowing through the fluid flow sensor. The collar comprises a body defining an interior that defines an airspace between the collar and the housing of the fluid flow sensor when the collar is positioned on the fluid flow sensor. The collar also includes a heat source secured to the body and adapted to heat air contained within the airspace to consequently heat the housing of the fluid flow sensor and the interior surfaces of the sensor to reduce condensation of the moist gas.

BACKGROUND OF THE INVENTION

The invention relates generally to flow sensors, and more particularly,to variable orifice fluid flow sensors.

Orifice flow sensors are used to measure the flow rates of fluids, whichinclude liquids and gases. A typical orifice flow sensor comprises afixed orifice through which a fluid is made to flow. A pressuredifference is established between the fluid that is present upstreamfrom the orifice and the fluid that is flowing through the orifice. Thispressure difference can be used to measure the flow rate of the fluid.For this purpose, a pressure transducer measures the pressure differencethat is established across the orifice, and is calibrated such that theflow rate of the fluid is calculated from this pressure difference.

Variable orifice flow sensors provide sufficient pressure difference formeasurement purposes across a broad range of flow rates. This isachieved by introducing a bending member into the fluid flow passage.The bending member is mounted to the housing for the fluid flow passageand includes a flapper that is positioned across the fluid flow passageand bends or flexes in the direction of the fluid flow as a result ofcontact with the fluid flow, and hence creates a variable orifice withinthe fluid flow passage. The measurement of flow rates in a variableorifice flow sensor is similar to the measurement of flow rates in fixedorifice flow sensors. That is, a pressure transducer measures thepressure difference across the variable orifice and calculates the flowrate of the fluid from the pressure difference.

U.S. Pat. Nos. 4,989,456; 5,033,312; 5,038,621; 6,722,211 and 7,270,143show variable orifice flow sensors.

Orifice gas flow sensors are commonly used for measuring flow rates inmedical applications, such as breathing apparatuses that deliver desiredquantities of breathing gases to a patient. When used to measurebreathing gases or recirculating breathing gases, the gases flowingthrough the sensor may contain moisture.

In the case where a gas flowing through a variable orifice flow sensorincludes moisture, the moisture may condense and form liquid dropletsthat may accumulate in the sensor, which can produce problems withconsistent and repeatable operation of the sensor, such as byinterfering with the flexing of the flapper, thereby impacting theaccuracy of the results obtained by the sensor.

BRIEF DESCRIPTION OF THE INVENTION

In the present invention a fluid flow sensor is provided having ahousing defining a fluid flow passage through the sensor. A collar isdisposed around the housing for the fluid flow sensor to define anairspace between the collar and the housing. A heating element isdisposed in the airspace and is operable to heat the air containedwithin the airspace to consequently heat the fluid flow passage abovethe dew point of the moist gas to correspondingly reduce condensation ofthe fluid flow within the fluid flow sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of a fluid flow sensor and collar inaccordance with an exemplary embodiment of the invention.

FIG. 2 is an isometric view of a collar in accordance with an exemplaryembodiment of the invention

FIG. 3 is a cross sectional view of a fluid flow sensor and collar inaccordance with an exemplary embodiment of the present invention.

FIG. 4 is an isometric view of a fluid flow sensor and collar inaccordance with another exemplary embodiment of the invention.

FIG. 5 is a cross sectional view of a fluid flow sensor and collar inaccordance with another exemplary embodiment of the invention.

FIG. 6 is an isometric view of a heat source in accordance with anotherexemplary embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 illustrates an isometric view of a fluid flow sensor 100 inaccordance with one embodiment of the present invention. Fluid flowsensor 100 is used to measure flow rates of fluids, such as moist gases,flowing through the fluid flow sensor 100, for example, by developingpressure differences within the fluid flow sensor 100 that are used tomeasure flow rates of the fluids. Fluid flow sensor 100 has a generallycylindrical configuration. However, fluid flow sensor 100 may be formedin a variety of shapes and sizes and still lie within the scope of thisinvention.

FIGS. 1-3 illustrate an exemplary embodiment of the fluid flow sensor100 comprising a housing 102 that defines a fluid flow passage 103therethrough having an inlet end 104 and an outlet end 106. When fluidflow sensor 100 is used for measuring gas flow rates in a breathingapparatus, the fluid flow sensor 100 is inserted at one or more desiredlocations in a breathing circuit where the breathing gas is introducedinto the housing 102 of the fluid flow sensor 100 through the inlet end104 to pass through the fluid flow passage 103 and exit though theoutlet end 106 to continue through the breathing circuit. Themeasurements made to determine the flow rate of the gas passing throughthe fluid flow sensor 100 are made as the gas passes through fluid flowpassage 103 in the housing 102 from the inlet end 104 to the outlet end106.

Disposed around the housing 102 of the fluid flow sensor 100 is a collar108. FIG. 2 shows the collar 108 comprising a body 109 including a firstportion 110 and a second portion 112. Collar 108 can be configured tocover some or all of the exterior of the housing 102 in order to heatthe interior surfaces of the fluid flow passage 103 of the housing 102.First portion 110 and second portion 112 of the collar 108 are eachformed of a suitable material, such as a plastic material, and includean outer wall 114, a pair of side walls 116 extending along andoutwardly from opposed sides of the outer wall 114 to define an interior118 within the first portion 110 and second portion 112. The firstportion 110 also defines a number of channels 120 that extend throughthe outer wall 114 and/or side walls 116 to enable tubes or hoses 122 orother items to be connected to the measurement ports 123 (FIG. 3) on thehousing 102 of the fluid flow sensor 100 through the first portion 110to allow determination of the fluid flow rate of the gas passing throughthe sensor 100.

Second portion 112 is formed with a recess 124 extending outwardly fromthe outer wall 114 in a direction generally opposite the side walls 116.Recess 124 is shaped to receive a heat source 126 therein, which isconnected via wires 128 extending through apertures 130 in the recess124 to a suitable power source and/or controller (not shown) foroperation of the heat source 126. Heat source 126 can take any suitableform, and in the illustrated exemplary embodiment is formed of aresistive heating element or coil 131.

First portion 110 and second portion 112 are joined to one another atone end by a suitable connector 132. Connector 132 enables the firstportion 110 and second portion 112 to be moved apart from one another toenable placement of the collar 108 around the housing 102 of the fluidflow sensor 100. The connector 132 can take any suitable shape orconfiguration and can enable first portion 110 and second portion 112 tobe completely separated from one another. In the exemplary embodiment ofFIGS. 1-3, the connector 132 is formed as a hinge 134, formed ofadhesive tape or other suitable hinge structure, engaged with adjacentends of first portion 110 and second portion 112 to enable pivotingmovement of first portion 110 and second portion 112 relative to oneanother.

Opposite hinge 134, the collar 108 includes a securing member 136capable of releasably engaging the ends of first portion 110 and secondportion 112 with one another. Securing member 136 can take any suitableform or configuration, such as a detent disposed on first portion 110engagable with a recess on second portion, and in the exemplaryembodiment of FIG. 2, securing member 136 takes the form of a piece ofadhesive tape 138 placed over and releasably engaged with adjacent endsof first portion 110 and second portion 112, while in FIG. 3, thesecuring member is illustrated in the exemplary embodiment as amechanical securing mechanism 139.

In operation, first portion 110 and second portion 112 are separatedfrom one another using the connector 132 to allow placement of collar108 around housing 102 of fluid flow sensor 100. First portion 110 andsecond portion 112 are subsequently moved towards one another to enablesecuring member 136 to secure first portion 110 and second portion 112to one another opposite connector 132. In this position, tubes 122 areconnected to housing 102 and routed through ports 120 in first portion110 to enable proper operation of fluid flow sensor 100. Engagement ofsecuring member 136 positions first portion 110 and second portion 112of collar 108 around the housing 102 such that the ends of outer walls114 and side walls 116 of first portion 110 and second portion 112 arepositioned adjacent one another to enable interiors 118 of first portion110 and second portion 112 to form an enclosed airspace 140 betweencollar 108 and housing 102.

In this position, heat source 126 can be operated to heat the air withinthe airspace 140 to a desired temperature. Heating of the air in theairspace 140 efficiently utilizes the heat from the heat source 126 toconsequently heat the entire perimeter of the portion of the housing 102in contact with the airspace 140 without any direct contact of the heatsource 126 with the housing 102. Heating of the housing 102 in thismanner heats the interior surfaces of the fluid flow passage 103 definedwithin the housing 102. This significantly reduces and can prevent anycondensation of moisture contained in the moist gas as it flows alongthe fluid flow passage 103 to the outlet end 106. This mode of heatingthe interior surfaces of the fluid flow passage utilizes less energy orpower as the heat source 126 is only directly heating the air within theairspace 140, and not the material forming the housing 102 for the fluidflow sensor 100.

When it is desired to remove and either replace or sterilize the fluidflow sensor 100, the collar 108 can be removed from the housing 102 bydisengaging the securing member 136 and displacing the first portion 110and second portion 112 away from one another. The fluid flow sensor 100can then be cleaned, sterilized and/or replaced and the collar 108 canbe re-attached to the fluid flow sensor 100 for further use, as thecollar 108 does not contact the sterile fluid flow passage 103 of thefluid flow sensor 100, and does not require sterilization.

In alternative exemplary embodiments, various sealing elements (notshown) can be secured to the edges of one or more of the outer walls 114and/or the side walls 116 of first portion 110 and second portion 112 ofthe collar 108 to engage the housing 102 and/or the walls 114, 116 ofthe other portion 110, 112 to more effectively retain air heated by theheat source 126 within the airspace 140 and consequently moreefficiently heat the interior surfaces of the fluid flow passage 103.

FIGS. 4-6 show another exemplary embodiment of the invention in whichthe collar 108 has outer wall 114 and side walls 116 formed as anenclosure 142 secured directly to and positioned around a portion of thehousing 102 to form a completely enclosed airspace 144 between thehousing 102 and the enclosure 142. The enclosure 142 can have anydesired shape and configuration, and in the exemplar) illustratedembodiment is integrally formed with the housing 102 with outer wall 114and side walls 116 such that the enclosure 142 and housing 102 form asingle component for the fluid flow sensor 100.

The housing 102 includes a connection and spacing post 146 disposed onand extending outwardly from the exterior of the housing 102 to which issecured one end of a heat source 148. The heat source 148 can be formedof any suitable heating element(s), similar to heat source 126. In theexemplary illustrated embodiment the heat source 148 is formed of aresistive strip heating element 150. The strip heating element 150 isspaced a distance from the housing 102 by the post 146 to avoid directcontact with the housing 102 to maximize the ability and efficiency ofthe strip heating element 150 in heating the air within airspace 144.Strip heating element 150 wraps around housing 102 within enclosure 142while maintaining a minimum space 151 between strip heating element 150and housing 102 and extends through an aperture 152 in enclosure 142.The portion of strip heating element 150 positioned outside of enclosure142 includes one or more electrical contacts 154 that are operablyconnected to a power source (not shown) and controller (not shown) inorder to enable and control operation of the strip heating element 150to heat the air within the airspace 144.

The various exemplary embodiments of the invention provide a collar 108that can be retrofit onto or incorporated within the structure of afluid flow sensor 100 and that is capable of heating the interiorsurfaces of the fluid flow sensor 100 to reduce condensation from themoist gas within the fluid flow sensor 100. In an alternative exemplaryembodiment of the invention, the heat source 126 could be spaced fromthe collar 108 such that the air heated by the heat source 126 could bedirected into the airspace 140 defined within the collar 108 along atube or other conduit-like member (not shown) in order to provide theheated air to the airspace 140 within the collar 108. In still, anotherexemplary embodiment of the invention, the collar 108 could be formed ofa flexible material that can be inflated by the introduction of theheated air into the airspace 140 defined between the collar 102 and thehousing 102 of the fluid flow sensor 100.

The written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A collar adapted for use with a fluid flow sensorto reduce condensation of a moist gas flowing through the fluid flowsensor, the collar comprising: a) a body defining an interior that isadapted to define an airspace with the fluid flow sensor when the bodyis positioned on the fluid flow sensor; and b) a heat source positionedwithin the interior of the body and adapted to heat air contained withinthe airspace.
 2. The collar according to claim 1 wherein the body isremovable from the fluid flow sensor.
 3. The collar of claim 2 whereinthe collar includes a first portion and a second portion engageable withone another.
 4. The collar according to claim 1 wherein the firstportion is detachable from the second portion.
 5. The collar accordingto claim 1 wherein the first portion is movably connected to the secondportion by a connector.
 6. The collar according to claim 5 wherein thefirst portion is releasably engaged with the second portion opposite theconnector by a securing member.
 7. The collar according to claim 1wherein the heat source is disposed within a recess formed on the body.8. The collar according to claim 1 wherein the body includes at leastone outer wall and a number of side walls extending outwardly from theouter wall and adapted to contact the fluid flow sensor.
 9. The collaraccording to claim 8 wherein the at least one outer wall includes anumber of ports adapted to receive tubes to be connected to the fluidflow sensor.
 10. The collar according to claim 1 wherein the body isfixed to the fluid flow sensor.
 11. The collar according to claim 10wherein the heat source is secured at one end to a post disposed on thefluid flow sensor.
 12. The collar according to claim 11 wherein the heatsource is positioned around the fluid flow sensor.
 13. The collar ofclaim 12 wherein the heat source is spaced from the fluid flow sensoralong its entire length.
 14. A fluid flow sensor comprising: a) ahousing that defines a fluid flow passage therethrough having an inletend and an outlet end; and b) a collar disposed around the housingbetween the inlet end and the outlet end, the collar comprising: i) abody defining an interior that defines an airspace in conjunction withthe housing; and, ii) a heat source secured to the body and adapted toheat air contained within the airspace.
 15. The fluid flow sensor ofclaim 14 wherein the collar is releasably secured to the housing. 16.The fluid flow sensor of claim 14 wherein the collar is fixed to thehousing.
 17. A method for reducing the condensation of a moist gaspassing through a fluid flow sensor, the method comprising the steps of:a) providing a fluid flow sensor comprising: i) a housing that defines afluid flow passage therethrough having an inlet end and an outlet end;and ii) a collar disposed around the housing between the inlet end andthe outlet end, the collar including a body defining an interior thatdefines an airspace in conjunction with the housing and a heat sourcesecured to the body and adapted to heat air contained within theairspace; b) operating the heat source to heat the air in the airspacebetween the heat source and the housing; and c) directing the moist gasthrough the fluid flow passage.
 18. The method of claim 17 furthercomprising the step of removing the collar from the fluid flow sensor.